1. Field of the Invention
This invention pertains to the field of mechanical clocks and, more particularly, to torsion pendulum clocks generally referred to as 400-day clocks, or anniversary clocks.
2. Description of the Related Art
Various designs and repair procedures for 400-day clocks are described in detail in a book entitled 400-Day Clock: Repair Guide by Charles Terwilliger (copyright 1991 by The Horolovar Company, Library of Congress Catalogue Card No. 83-81592). Although commonly called 400-day clocks, or anniversary clocks, they are mechanically categorized as torsion pendulum clocks.
Torsion pendulum clocks use a mainspring as the power source. Timing is maintained by the pendulum. The mainspring provides power to a ratchet mechanism for urging an escapement wheel into rotational motion. The ratchet mechanism includes an anchor that oscillates or "rocks" about a midpoint. The anchor includes distal pallets that engage teeth on the escapement wheel. As the anchor rocks back and forth, alternate pallets engage teeth of the escapement wheel. Thus, as the anchor goes through its rocking motion, one of the pallets disengages an escapement wheel tooth while the opposite pallet engages a tooth. During a single rocking motion of the anchor, the escapement wheel will advance a rotational distance equal to one-half tooth.
Additionally, the mainspring maintains torque on the escapement wheel. The wheel, in turn, urges the anchor into its rocking motion through minute impulses on the pallets. The anchor's rocking motion is communicated to an anchor pin which is mounted atop the anchor. A suspension fork, having tines on either side of the anchor pin, is fixedly connected to a suspension spring which suspends the torsion pendulum. Thus, the energy from the mainspring is converted into discrete impulses that cause an alternating rotation of the suspension spring which in turn oscillates the pendulum.
One of the most difficult adjustments associated with torsion pendulum clocks is setting the "beat." A clock is in beat when the impulses provided from the mainspring through the ratchet mechanism to the suspension fork are synchronized to occur symmetrically about a neutral position. (The neutral position is defined as the position the pendulum and suspension spring would assume when in static equilibrium, i.e., hanging without motion.) The tiny impulses from the ratchet mechanism to the fork (and thus the suspension spring) must occur at the exact same distance from the neutral position in order to maintain oscillation of the pendulum. Clocks which are even minutely out of beat will eventually stop running.
In all prior art clocks, beat was adjusted by turning the entire suspension system comprising the pendulum, suspension spring, and the suspension fork to align the fork relative to the anchor pin. Two principal methods were used to turn the suspension system. In a few older clocks, the suspension spring suspended from a fixed saddle, and it was thus necessary to adjust the suspension spring by twisting it until it deformed.
All 20th century clocks provide an adjustable saddle which includes a friction fit or a set screw that can be loosened. The adjustable saddles permit rotation of the suspension spring, fork, and pendulum. Although superior to the previous method, such adjustment is a delicate operation requiring very precise and skillful work.
A beat setting tool, disclosed in U.S. Pat. No. 196,385, provides a lever advantage for turning the saddle. Although helpful, this tool does not substantially assist with the precision required for setting the clock's beat. What is needed then is an easy and reliable apparatus for precise and accurate adjustment of the beat in torsion pendulum clocks.